This invention relates in general to a riser and in particular to an adapted version of a shuttle valve for connecting passageways between a riser and a tree in a subsea well.
A conventional subsea wellhead assembly includes a wellhead housing which supports one or more casing hangers located at upper ends of strings of casing extending into the well. A tubing hanger lands in the wellhead housing above the casing hanger and supports a string of production tubing that extends through the smallest diameter casing. The tubing hanger has a production bore which is offset slightly from the longitudinal axis. An annulus bore also extends through the tubing hanger, parallel to and offset from the axis, for communicating the tubing annulus to above the tubing hanger. The annulus bore is needed during installation of the tubing hanger and tubing to establish circulation down the tubing and back up the annulus. After the well has been completed, a removable plug is installed in the annulus bore, then a production tree is mounted to the wellhead housing. Access through the production tree to the tubing may be made for various workover operations that are needed.
Operators have begun installing a different type of wellhead assembly, referred to generally as a horizontal tree. In a horizontal tree, the tubing hanger lands in the tree, not in the wellhead housing located below the tree. The tubing hanger has a laterally extending production passage that registers with a passage in the tree. A bypass passage for tubing annulus access extends around the tubing hanger.
Various proposals have been made concerning workover operations on horizontal trees. Generally, the proposals suggest installing a monobore riser on the horizontal tree head. An annulus circulation line that is either separate or integrated with the monobore riser extends to the surface. The annulus circulation line communicates with an annulus circulation port in the horizontal tree above the tubing hanger.
A subsea test tree or riser connector is affixed on an upper end of a tree. The subsea test tree has a production passage and a port that is in communication with an annulus passage in the horizontal tree.
An internal tree cap is located within the tree. A production passage passes through the internal tree cap, and an annulus passage communicates with the annulus passage of the tree.
A shuttle valve is located within a valve receptacle or valve cylinder in an upper end of the annulus passage. The valve cylinder is in communication with an upper surface of the internal tree cap. A portion of the shuttle valve extends above the upper surface of the internal tree cap so that the shuttle valve opens when the subsea test tree or riser connector lands on the top of the internal tree cap. A spring or other suitable device biases the shuttle valve upwards, or in a closed position. Alternatively, the shuttle valve may be hydraulically actuated.